1. Field of the invention
The present invention relates to a mobile terminal with plural antennas. More particularly, the present invention relates to a mobile terminal of a certain size with plural antennas.
2. Description of the Related Art
Recently, as the functions of a mobile terminal are diversified, mobile terminals provide diverse services such as wireless Internet connections, digital multimedia broadcasting (DMB) for viewing programs of terrestrial and satellite origin, global positioning system (GPS) receivers, camera, MP3 players, and, radio frequency identification systems (RFID), as well as the communications function.
To use the diverse additional functions other than communications, multi-band mobile terminals are being developed, and to implement the multi-band mobile terminals, an antenna capable of transmitting and receiving a multi-band radio signal is needed. Such antennae may require features such as compact size, broad bandwidth and high gain.
In general, a mobile terminal is mounted with an external antenna or an internal antenna. A mono-pole antenna and a helical antenna are mainly used as external antennae, and a planar inverted F antenna (PIFA) is mainly used as internal antennae.
The mono pole antenna and the helical antenna are externally exposed so that the antenna can be damaged by an external impact. When a user uses the mobile terminal, the antenna is often located around the head of the user so that electromagnetic waves can possibly have a bad effect on the user.
To solve weakness of the external antenna, the PIFA internal antenna is often used.
Referring to FIG. 1, the PIFA 10 is implemented as a three-dimensional structure including a ground 5, a radiation part 11, a feeding part 15 and a short part 13.
The radiation part 11 is formed on the upper part of the ground 5, and the short part 13 is formed at the edge of the radiation part 11 to connect the ground 5 and the radiation part 11. The feeding part 15 supplies an electric current to the radiation part 11. Generally, impedance matching is determined according to the location of the short part 13 and the length of the feeding part 15.
As such, the PIFA 10 is an internal antenna which can be embedded in a mobile terminal, the weakpoints of the external antenna can be essentially solved, and manufacturing the internal antenna is easier than the external antenna. However, the PIFA 10 has the limit to miniaturization due to a gap between the radiation part 11 and the ground 5.
Meanwhile, to support functions, such as DMB, GPS and RFID, provided in different frequency bands, respectively, separate antennas are required. However, if the mobile terminal is mounted with plural PIFA antennas to support such functions, the size of the mobile terminal gets larger or the number of the PIFAs mounted in the mobile terminal is limited due to lack of space.
Recently, a planar antenna has been suggested for mobile communications. The planar antenna can be formed on the printed circuit board (PCB) so that extra space to place the antenna is rarely needed. However, because of the nature of the planar antenna, it is difficult to use with directional services so that it can not be put to practical use for mobile communications.